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. The rate and degree of change that is predicted to take place in arctic systems is without precedent, so assessments of what might happen, such as those that follow, are based on educated “guesses” rather than concrete data. However, it is certain that changes will take place in biological communities if even some of the climate-change predictions are correct and past evidence indicates that arctic species, especially larger vertebrates, are very likely to be vulnerable to extinction if climate warms. Many of these animals have evolved in response to global cooling throughout the last 5 million years or so and because of the speed with which change is predicted to occur it is most likely that relocation (i.e. changes in distribution) rather than adaptation within species, will be the major mode by which change will take place in biotic communities throughout the Arctic. In Svalbard the marine mammal fauna is much richer than that found in the terrestrial environment with 19 species occurring with regularity, 9 of which live in the area full-time, while the others are seasonal migrants. Polar bears are the top predator in this system. This species is intimately tied to the sea ice and any alteration to sea ice distribution or its character will affect polar bears. They hunt ringed seals, and other ice-associated seals, and also use ice corridors to move from one area to another. Pregnant females build their birth dens in thick snow cover on land, or on sea ice in some areas, and require good spring ice conditions when they emerge after many months without eating, with their dependent cubs. The first impacts of climatic warming on polar bears are already being seen at the southern limits of the bears’ distribution in areas such as James Bay and Hudson Bay where bears are thinner than in the past and fewer cubs are being born. If there is no summer sea ice, which is a high probability in ACIA climate scenarios, the only option available to polar bears would be a terrestrial summer life-style similar to brown bears, from which they evolved. But, polar bear experts suggest that if sea ice declines in the manner currently predicted by climate change models, it is unlikely that polar bears will survive as a species. Ice-living seals are also very dependent on the on the nature and extent of sea ice. They depend on this habitat for pupping, moulting and resting, and some species also do a lot of their foraging on ice-associated prey species. Ringed seals are the most numerous seal in Svalbard, and perhaps the most vulnerable of the high arctic pinnipeds to climate change because so many aspects of their life-history and distribution are tied to sea ice. They also require sufficient snow cover to construct lairs to keep their very small pups warm enough and the ice must be stable long enough in the spring season to successfully wean their young. Ringed seals do not normally haul out on land and performing this behaviour would be a rather dramatic change to the species behavioural repertoire. Land-breeding would expose the ringed seals’ small neonates to much higher predation rates, even in a best case scenario. The distribution, density, and reproductive success of the other resident ice breeding seals, the bearded seal and the walrus, also depends on suitable sea ice conditions being present in shallow, often coastal, areas where benthic communities produce enough food to support them. However, both of these species do haul out on land during the summer months in some areas, and might adjust to land breeding more readily than ringed seals. Harp seals and hooded seals are seasonal visitors in Svalbard. These species are flexible about the nature the summer ice habitat, but during breeding they travel to traditional sites in southern waters where they form herds in extensive pack ice areas. During poor-ice years massive pup mortality occurs in these species. It is difficult to predict whether harp and hooded seals will adjust the location of their breeding and moulting activities if spring ice distributions change dramatically over a relatively short time interval. Unlike the seals discussed above, climate warming is likely to be very positive for the small population of harbour seals breeding in Svalbard. They are for the most part temperate species that have a sufficiently broad feeding niche that they can occupy some warm-spots even in the current climate conditions within the Arctic. Each of the three resident arctic whales in Svalbard exhibit modestly specific habitat selection with varying amount of ice cover, depths, bathymetric structure etc. playing a role in where they reside. Bowhead whales depend on calanoid copepods and euphausiids for their food and changes in sea-ice conditions are likely to have a major impact on bowhead whale foraging. It is not known whether this most highly adapted ice-cetacean could adjust to ice-free waters. Narwhal and beluga also spend a lot of their time associated with ice, and are known to forage at ice edges and cracks. But, these two species also range well south of summer ice edges and in Svalbard belugas do most of their foraging, at least in summer, along the fronts of glaciers. Climate change impacts on these species are likely to be mediated through ice distribution patterns and their affects on key prey species; killer whale predation would be expected to increase when there is less ice. All of the other cetacean species that frequent Svalbard avoid ice-covered areas (pilot whales, sperm whales, white-beaked dolphins, killer whales, northern bottle-nosed whales, minke whales, fin whales, humpback whales and blue whales) and their distributions are predominantly determined by prey availability. If marine productivity increases as the seasonal ice cover diminishes, it is likely that more cetacean species will spread northward from temperate waters toward Svalbard. Some arctic marine mammals may not survive in a warmer Arctic. Buta warmer Arctic with a longer growing season will in all probability be a more productive system, that afford new opportunities to other species. Additionally, the unexpected versatility of species should not be forgotten. The scope for adaptability among animal species is often vast, and we should not underestimate the potential of at least some arctic marine mammals to adjust to a new climatic regime in the Arctic.
©
2004 Center for International Climate and Environmental Research - Oslo
(CICERO). All rights reserved. |
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